If the retirement age is 58 years in your organisation, the employee has to retire on attaining the age of 58.
If the services of the retired employee is needed by the organisation, after his retirement and settlement of all dues,
he may be re-employed on contract basis for a specific period, on mutually agreed terms.
Engaging a person, who has retired from any other organisation , on contract basis, on mutually agreed terms, for a specific period is also possible.